{
\def\sym#1{\ifmmode^{#1}\else\(^{#1}\)\fi}
\begin{tabular}{l*{4}{c}}
\hline\hline
            &\multicolumn{1}{c}{(1)}&\multicolumn{1}{c}{(2)}&\multicolumn{1}{c}{(3)}&\multicolumn{1}{c}{(4)}\\
            &\multicolumn{1}{c}{l\_volume}&\multicolumn{1}{c}{l\_volume}&\multicolumn{1}{c}{l\_volume\_adh}&\multicolumn{1}{c}{l\_volume\_adh}\\
\hline
mode\_cost\_1987&      -3.660\sym{a}&      -3.502\sym{a}&      -5.382\sym{a}&      -3.459\sym{a}\\
            &     (0.140)       &     (0.151)       &     (0.182)       &     (0.150)       \\
\hline
\(N\)       &        2473       &        1635       &        4356       &        1635       \\
r2\_a        &       0.540       &       0.516       &       0.551       &       0.516       \\
r2\_p        &                   &                   &                   &                   \\
\hline\hline
\multicolumn{5}{l}{\footnotesize Standard errors in parentheses}\\
\multicolumn{5}{l}{\footnotesize \sym{c} \(p<0.1\), \sym{b} \(p<0.05\), \sym{a} \(p<0.01\)}\\
\end{tabular}
}
